Fructose-1,6-bisP OA Acetyl CoA • Fig. 39.12 Metabolic pathways in hepatocytes during digestive (“D” numbers) and fasting (“F” numbers) phases. Reactions/pathways: 1D, glucokinase; 1F; G6Pase; 2D, glycogen synthesis; 2F, glycogenolysis; 3D, phosphofructokinase 1; 3F, fructose-1,6-bisphosphatase; 4D, glucose-6-phosphate dehydrogenase; 5D, pyruvate kinase; 6D, pyruvate dehydrogenase; 6F, pyruvate carboxylase; 7F, phosphoenolpyruvate carboxykinase; 8D, ATP-citrate lyase; 9D, acetyl CoA carboxylase; 9F, malonyl CoA decarboxylase; 10D fatty acid synthase; 11D, glycerol phosphate/fatty acyl CoA transferase and other enzymes involved in esterification and formation of TG; 12D, inhibition by malonyl CoA (Mal CoA) of fatty acyl CoA transporter, carnitine/palmitoyl transporter 1 (CPT1) on outer mitochondrial membrane; 13F, movement of fatty acyl CoA into mitochondrion through CPT1 and  beta-oxidation to acetyl CoA.
sympathetic response through the hypothalamus. The direct metabolic actions of catecholamines are mediated primarily by α1-, β2-, and β3-adrenergic receptors located on muscle, adipose, and liver tissue (see later). Like the glucagon receptor, β-adrenergic receptors (β2 and β3) increase intracellular cAMP. The α1-adrenergic receptor is also expressed by some organs, especially the liver.
Hormonal Regulation of Specific Metabolic Reactions and Pathways
This section discusses the main pathways in hepatocytes, skeletal myocytes, and adipocytes that contribute to integrated metabolism. For even more detailed description, the student is referred to biochemistry textbooks.
Hepatocyte Metabolism: Digestive vs. Fasting Phases
Some of the key metabolic steps regulated by insulin and glucagon (and catecholamines) in the liver are as follows (refer to